This study is a withdrawal randomized clinical trail to evaluate the clinical efficacy and safety of 1.1 chemical drugs N-acetyl glucosamine on Chinese IBS-D patients coming from four centers in chongqing. 180 IBS-D patients in this research are accord with the Rome III diagnostic criteria, screening/import period pain intensity scores of the NRS week mean value are 3.0 plus and the days which at least more than one time a stool type are 6 or 7 type over 2 days/week. Test cycle includes screening/import period (2 weeks), open treatment period (8 weeks), a double-blind placebo-controlled randomized withdrawal period (8 weeks), the main outcome measures are pain intensity (NRS score 11 point scale) and stool type ( Bristol type). And secondary endpoints included overall symptoms sensory scores, defecation frequency, abdominal distension, mucous stool and quality of life parameters (IBS-36 scale). After the end of the treatment period, the participants whose pain intensity and stool type are effective subjects into a randomized withdrawal period, analysis and comparison of the difference between treatment group and placebo group withdrawal rate and curative effect index score reduces.

Inclusion Criteria:

• Man or woman, aged 18 to 65 years, inclusive.
• Based on the Roman III diagnostic criteria for diagnosis of IBS-D subjects, recurrent abdominal pain or discomfort (hard to describe the discomfort of pain), monthly attack within the past 3months at least 3 days. With two or more of the following three kinds of symptoms:

At least a portion of the time abdominal pain or defecate increase when discomfort.

At least a portion of the time abdominal pain or the row of loose stools when discomfort.

At least a portion of the time abdominal pain or discomfort improved after defecation.

Symptoms for at least 6 months before diagnosis

• Screening/import period pain intensity scores of the NRS week mean value are 3.0 plus and the days which at least more than one time a stool type are 6 or 7 type over 2 days/week.
• Voluntarily signed the informed consent form

Exclusion Criteria:

• The absorption of any known adverse
• History of gastrointestinal surgery ( not including appendectomy)
• History of organic gastrointestinal diseases: IBS, cancer etc.
• History of chronic diseases: anemia (hemoglobin<90g/L), pulmonary tuberculosis, diabetes or cardiovascular, liver, kidney, brain, and hematopoietic system and other serious diseases and psychiatric patients, AST(aspartate aminotransferase), ALT (alanine aminotransferase)> 1.5 times, BUN (blood urea nitrogen)> 1.2 times, Cr > 1.0 times normal.
• The disease of lactose intolerance, gallstones, endometriosis, easily confused with IBS symptoms of ;
• Progressive weight loss;
• Concomitant medication is unable to stop but affect the gastrointestinal movement and function in the experiment, such as antibiotic drugs, the drugs of regulating the intestinal microecology;
• Concomitant medication use continuously for more than a week but affect the gastrointestinal movement and function in the experiment, such as parasympathetic inhibitors, nondepolarizing agent, antidiarrheal, opioid formulation, etc;
• Other researchers think not suitable for the list;